A portable electronic device represented by a notebook-sized personal computer or a mobile communication device is equipped with a microprocessor of processing multimedia information.
This kind of microprocessor tends to rapidly increase a heating value during operation in conjunction with increasing computing speed and multifunctionality.
For that reason, it is necessary, for the sake of stably assuring the operation of the microprocessor, to improve its cooling capability to meet that heating value.
As for an electronic device represented by a semiconductor laser source apparatus, it is necessary to exert temperature control over a semiconductor which is an oscillation source to an adequate temperature from a perspective of implementing higher power and securing wavelength stability of a beam.
Because of demands for miniaturization in recent years, a temperature controller thereof is required to be miniaturized and have high temperature control performance.
As for a display apparatus represented by a projection display apparatus of irradiating an image modulated into video signals on a light valve with illumination light and projecting the image by enlarging it on a screen with a projection lens, a display device comprised of a high-resolution light valve is used therein in order to project image information more clearly, and higher luminance for a brighter projection screen is further promoted.
The display device of the projection display apparatus required to be high-luminance absorbs heat of the light of components not effectively projected on the screen against incident light in principle. Therefore, heating of the display device limits an increase in the luminance.
As a countermeasure against it, a reflective display device of a liquid crystal and so on is increasingly used instead of a transmissive liquid crystal display device.
Even in the case of the reflective display device, a slight light absorption occurs. Therefore, it is necessary to forcibly cool the reflective display device.
For this reason, use is increasingly made of a cooling apparatus having integrated an adjustment mechanism of accurately positioning the reflective display device, a cooling element of forcibly cooling the reflective display device, a heat sink of cooling a radiating side of the cooling element and a cooling fan of air-cooling the heat sink.
Hereunder, a concrete description will be given as to a conventional technique relating to heat countermeasures of the electronic device and display apparatus.
Here, the description will be given by taking an example of a cooling apparatus of the projection display apparatus using a general reflective display device.
An optical system of the projection display apparatus is basically comprised of a light source lamp unit, a display device comprised of a reflective liquid crystal panel of color-separating white light from the light source of the light source lamp unit into red (R) green (G) and blue (B) and modulating these rays according to the image information, an optical unit of color-composing the modulated light, and a projection lens unit of projecting the color-composed light by enlarging it on the screen.
Recently, a high-resolution display device is increasingly used for the projection display apparatus in order to project image information more clearly, and higher luminance for the brighter projection screen is further promoted as described above.
A description will be given by using FIGS. 10 and 11 as to an example of a conventional 3-light value projection display apparatus using reflective display devices of R, G and B and a cooling apparatus thereof.
First, FIG. 10 is a diagram showing a schematic configuration of a conventional projection display apparatus.
The conventional projection display apparatus is comprised of a light source lamp unit 1 which is a light source of projecting the image information by optically enlarging it, a filter 2 of eliminating infrared rays and ultraviolet rays from the light of the light source lamp unit 1 and transmitting only visible light, an irradiation optical unit 3 of focusing the visible light from the filter 2, a color separation and composition prism unit 5 of color-separating the light focused by the irradiation optical unit 3 after passing a reflecting prism unit 6 to lead it to reflective display devices 4a, 4b and 4c and also color-composing the light optically generated as the image information by the reflective display devices 4a, 4b and 4c, and a projection lens unit 7 of enlarging and projecting the image information composed by the color separation and composition prism unit 5 which is reflected by the reflecting prism unit 6.
The light source lamp unit 1 is comprised of a superhigh pressure mercury lamp 1a generally having high luminous efficiency and a concave mirror 1b of efficiently focusing the light.
The color separation and composition prism unit 5 of color-separating and color-composing the light from the light source lamp unit 1 into R, G and B is comprised of a blue-reflecting dichroic mirror, a red-reflecting dichroic mirror and a green-transmitting dichroic mirror of selecting the white light wavelength-wise for instance.
The white light is color-separated into R, G and B from their respective coating characteristics to be led to the reflective display devices 4a, 4b and 4c of R, G and B respectively. And the light modulated into the image information by the reflective display devices 4a, 4b and 4c is composed again by the color separation and composition prism unit 5.
The reflecting prism unit 6 is an integral prism of a so-called half-mirror configuration of transmitting the light from the irradiation optical unit 3 and leading the light color-composed by the color separation and composition prism unit 5 to the projection lens unit 7.
FIG. 11 is a schematic sectional view showing the cooling apparatus of the conventional reflective display device.
FIG. 11 shows only the reflective display device 4c. And, the reflective display device 4a and 4b also have the same configuration.
The reflective display device 4c has its one surface joined and fixed by an adhesive to a position adjustment mechanism 8 capable of planar position adjustment and focus adjustment. The position adjustment mechanism 8 is accurately positioned and fixed by joining or by an adhesive to the color separation and composition prism unit 5.
The other surface of reflective display device 4c is joined to a thermoelectric cooling element 9 comprised of a semiconductor via a holder 10 also playing a role of thermal conduction.
The thermoelectric cooling element 9 has a heat sink 11 for its radiation joined thereto, and the heat sink 11 has a cooling fan 12 of cooling it joined thereto.
The cooling fan 12, heat sink 11 and holder 10 are integrally assembled with screws and so on (not shown).
As for the conventional cooling apparatus as described above, however, a larger volume of light is focused on the reflective display devices 4a, 4b and 4c in the case of the projection display apparatus targeting higher luminance. Therefore, it is necessary to improve the cooling capability.
For that reason, the thermoelectric cooling element 9, heat sink 11 and cooling fan 12 having higher capability become necessary, which leads not only to growth in size of the apparatus but also to an increase in weight thereof.
As the cooling apparatus needs to radiate a total heating value of the heating value of power consumption meeting an endothermic amount of the thermoelectric cooling element 9 and the heating value of the reflective display devices, the cooling fan 12 becomes larger than expected.
As the cooling fan 12 is joined to the heat sink 11, draft resistance may become excessive leading to louder blast noise.
In the case where the endothermic amount of the thermoelectric cooling element 9 is increased, the holder 10 of functioning as a thermal conduction member may have dew condensation generated thereon because a junction side of the thermoelectric cooling element 9 reaches temperature significantly lower than ambient temperature.
Because of the structure of the cooling fan 12, a central portion thereof is a motor drive portion of the cooling fan 12 so that only outer portions of the heat sink 11 are cooled by draft as indicated by arrows in FIG. 11 and cooling efficiency of the heat sink 11 is apt to be deteriorated.
In view of radiation routes, there are three material junctions between the reflective display device 4c and the holder 10, between the holder 10 and the thermoelectric cooling element 9, and between the thermoelectric cooling element 9 and the heat sink 11.
For this reason, an impedance of heat transfer, that is, a thermal resistance becomes so high that very high radiation capability must ordinarily be designed.
Furthermore, driving power of the light source lamp unit is becoming higher in conjunction with the higher luminance of the projection display apparatus in recent years.
Endothermic capability of the thermoelectric cooling element 9 is generally less than 50 percent.
For this reason, the thermoelectric cooling element 9 requires electric power of twice to six times of the heating value of the reflective display device 4c so that its power consumption is extremely high.